She immediately swung around and snatched the phone from his hand, she said, and started to shout about what he'd done.

The crowd came to her defence, holding the guy off so she could run with away with his phone and bring it to police.

"When I got there, I handed the phone and the picture and him in as well, because he'd followed me, and they kind of said, 'Sorry, there's nothing we can do about this,'" she said.

Shocked, she went home and did some research and learned that upskirting wasn't considered a sexual offence in England and Wales, and that there was nothing on the books that would allow authorities to easily prosecute it.

"That's when I realized, OK, we need to update the law here, we need to change it," she said.

Lobbying lawmakers, one at a time

She teamed up with a law firm that took on her cause for free, and they proceeded to lobby lawmakers "one by one," she said.

"We managed to get MPs and politicians and ministers from every party to agree with us — and that's what really made the difference, because there's not many things in British politics right now that everyone agrees on, you know," she said.

She garnered more than 500,000 signatures on a petition. It took her a day and a night to read all the comments from other women who had similar experiences.

"Immediately, I knew it was a way bigger problem than we'd given it credit for," Martin said. "And then I started receiving stories as well, and that really bolstered me to keep going."

Private member's bill stalled

The path toward approval was complex because the proposed law was first introduced by a legislator interested in Martin's case, not by the government. A private member's bill can be choked off by a single objection in Parliament.

That happened in June when Conservative Party lawmaker Christopher Chope objected.

He later said he supported Martin, but objected in principle to private members' bills being brought before Parliament on a Friday without enough time for a full debate.

U.K. Prime Minister Theresa May's government decided to introduce the measure, giving it the backing needed to sail through Parliament.

"He kind of helped in terms of objecting to it, because it made people care about it way more," Martin said.

No one has the right to take pics under your clothes, without permission.<a href="https://twitter.com/ginamartin_uk?ref_src=twsrc%5Etfw">@ginamartin_uk</a>'s inspiring campaign to stop upskirting has been passed in <a href="https://twitter.com/UKHouseofLords?ref_src=twsrc%5Etfw">@UKHouseofLords</a>.<br><br>Final step is Royal Assent - which is where the law changes.<a href="https://twitter.com/hashtag/UpskirtingLaw?src=hash&amp;ref_src=twsrc%5Etfw">#UpskirtingLaw</a> | <a href="https://twitter.com/hashtag/ItsNotOk?src=hash&amp;ref_src=twsrc%5Etfw">#ItsNotOk</a><a href="https://t.co/khQTebGTa2">https://t.co/khQTebGTa2</a>

Martin said she was compelled to take on this fight because she was tired of excusing harassment in her daily life.

"Like, walking down the street and someone yelling something from a car, or being in a bar and someone smacking my bum or, you know, some guy asking me out and me saying, 'No, I'm OK, thank you,' and him not taking no for an answer," she said.

"It'd been too many instances where I'd kind of go, 'OK, I'll brush it off, that's just life,' and I think something kind of snapped in me this time and I just went, 'Do you know what? I'm not doing this again.'"

The law will apply in England and Wales. The practice is already banned in Scotland.

Written by Sheena Goodyear with files from Associated Press. Interview with Gina Martin produced by Sarah Jackson.